Antilock brake systems (ABS) are generally installed in vehicles. Antilock brake systems are systems that stabilize steering of the vehicle and perform brake control such that the braking distance becomes as short as possible by easing up on the wheel brake force to eliminate skidding when it has been detected that the wheels are skidding at the time of braking and thereafter again increasing the brake force. Antilock brake systems are mainly configured from a hydraulic pressure modulator, wheel speed sensors, and an electronic control unit (ECU). The ECU processes signals, controls actuators inside the hydraulic pressure modulator, and controls the brake pressure. Generally, in antilock brake systems, the ECU judges the skidding tendency of the braked wheels on the basis of wheel speed signals from the wheel speed sensors and, when it judges that the braked wheels are in a skidding tendency, outputs a control signal to the modulator that adjusts the brake pressure. Thus, the modulator adjusts the brake pressure such that skidding of the braked wheels is eliminated.
ABS software ordinarily models ABS braking, and a control program is designed in accordance with that model. Various parameters are used in the ABS control program. By optimizing (calibrating) these parameters, ABS braking following the model is realized. The parameters used in ABS control vary depending on ABS braking models and control algorithms, but a parameter relating to the operating characteristic of the hydraulic pressure modulator, a parameter required by the ABS braking model, and a parameter relating to the braking characteristic of the vehicle are possible. These parameters relating to ABS control can be tentatively decided by the specifications of each component and simulations at the early design stage. However, it is not always the case that optimum ABS braking will be obtained with parameters that have tentatively been set by simulations or the like. For that reason, ABS braking tests are performed using an actual vehicle equipped with ABS software in which tentative parameters have been set, wheel speed, hydraulic pressure, and vehicle motion during ABS braking are measured, and each parameter is optimized (calibrated) on the basis of these actual measured values such that optimum ABS braking is obtained.